A Study to Learn if a Combination of Fianlimab and Cemiplimab Versus Cemiplimab Alone is More Effective for Adult Participants With Advanced Non-Small Cell Lung Cancer (NSCLC)

Key Inclusion Criteria:

1. Patients with non-squamous or squamous histology NSCLC with stage IIIB or stage IIICdisease who are not candidates for surgical resection or definitive chemoradiationper investigator assessment or stage IV (metastatic disease), who received no priorsystemic treatment for recurrent or metastatic NSCLC.

2. Availability of an archival or on-study formalin-fixed, paraffin-embedded (FFPE)tumor tissue sample, without intervening therapy between biopsy collection andscreening as described in the protocol

3. For enrollment in phase 2, patients should have PD-L1 levels ≥ 50%, as determined bya College of American Pathologists (CAP)/Clinical Laboratory Improvement Amendments (CLIA) (or equivalently licensed, according to local regulations) accreditedlaboratory, as described in the protocol. For enrollment in phase 3, patients shouldhave expression of programmed cell death ligand-1 (PD-L1) in ≥50% of tumor cellsstained using an assay performed by a central laboratory, as described in theprotocol.

4. At least 1 radiographically measurable lesion by computed tomography (CT) ormagnetic resonance imaging (MRI) per Response Evaluation Criteria in Solid Tumorsversion 1.1 (RECIST 1.1) criteria. Target lesions may be located in a previouslyirradiated field if there is documented (radiographic) disease progression in thatsite.

5. Eastern Cooperative Oncology Group (ECOG) performance status of ≤1.

6. Adequate organ and bone marrow function, as described in the protocol.

Key Exclusion Criteria:

1. Patients who have never smoked, defined as smoking ≤100 cigarettes in a lifetime.

2. Active or untreated brain metastases or spinal cord compression. Patients areeligible if central nervous system (CNS) metastases are adequately treated, andpatients have neurologically returned to baseline (except for residual signs orsymptoms related to the CNS treatment) for at least 2 weeks prior to enrollment.Patients must be off (immunosuppressive doses of) corticosteroid therapy.

3. Patients with tumors tested positive for actionable epidermal growth factor receptor (EGFR) gene mutations, anaplastic lymphoma kinase (ALK) gene translocations, orc-ros oncogene 1 (ROS1) fusions, as described in the protocol.

4. Encephalitis, meningitis, or uncontrolled seizures in the year prior to enrollment.

5. History of interstitial lung disease (eg, idiopathic pulmonary fibrosis ororganizing pneumonia), of active, noninfectious pneumonitis that requiredimmune-suppressive doses of glucocorticoids to assist with management, or ofpneumonitis within the last 5 years. A history of radiation pneumonitis in theradiation field is permitted as long as pneumonitis resolved ≥6 months prior toenrollment.

6. Known primary immunodeficiencies, either cellular (eg, DiGeorge syndrome,T-cell-negative severe combined immunodeficiency [SCID]) or combined T- and B-cellimmunodeficiencies (eg, T- and B-cell negative SCID, Wiskott Aldrich syndrome,ataxia telangiectasia, common variable immunodeficiency).

7. Ongoing or recent (within 2 years) evidence of significant autoimmune disease thatrequired treatment with systemic immunosuppressive treatments, which may suggestrisk of immune-mediated treatment-emergent adverse events (imTEAEs). Patients withuncontrolled type 1 diabetes mellitus or with uncontrolled adrenal insufficiency areexcluded. The following are not exclusionary: vitiligo, childhood asthma that hasresolved, residual hypothyroidism that required only hormone replacement, orpsoriasis that does not require systemic treatment.

8. Patients with a condition requiring corticosteroid therapy (>10 mg prednisone/day orequivalent) within 14 days of randomization. Physiologic replacement doses areallowed even if they are >10 mg of prednisone/day or equivalent, as long as they arenot being administered for immunosuppressive intent. Patients with clinicallyrelevant systemic immune suppression within the last 3 months before trialenrollment are excluded. Inhaled or topical steroids are permitted, provided thatthey are not for treatment of an autoimmune disorder.

9. Patients who have received prior systemic therapies are excluded with the exceptionof the following:

10. Adjuvant or neoadjuvant platinum-based doublet chemotherapy (after surgeryand/or radiation therapy) if recurrent or metastatic disease develops more than 6 months after completing therapy as long as toxicities have resolved to CTCAEgrade ≤1 or baseline with the exception of alopecia and peripheral neuropathy.

11. Anti-PD-(L) 1 with or without LAG-3 as an adjuvant or neoadjuvant therapy aslong as the last dose is >12 months prior to enrollment.

12. Prior exposure to other immunomodulatory or vaccine therapies as an adjuvant orneoadjuvant therapy, Cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA-4)antibodies as long as the last dose is >6 months prior to enrollment.Immune-mediated AEs must be resolved to CTCAE grade ≤1 or baseline by the timeof enrollment. Endocrine immune-mediated AEs controlled with hormonal or othernon-immunosuppressive therapies without resolution prior to enrollment areallowed.

Note: Other protocol-defined Inclusion/ Exclusion Criteria apply.